Semiconductor device including MOS field effect transistor having offset spacers of gate sidewall films on either side of gate electrode and method of manufacturing the same

ABSTRACT

First and second impurity doped regions are formed in a semiconductor substrate. A first gate electrode is formed on the first impurity doped region with a first gate insulation film interposed therebetween. A second gate electrode is formed on the second impurity doped region with a second gate insulation film interposed therebetween. A first sidewall insulation film is formed on either side of the first gate electrode. A second sidewall insulation film has a thickness different from that of the first sidewall insulation film and are formed on either side of the second gate electrode. A third sidewall insulation film is formed on the first sidewall insulation film on the side of the first gate electrode. A fourth sidewall insulation films have a thickness different from that of the third sidewall, insulation film and are formed on the second sidewall insulation film on the side of the second gate electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.11/106,472, filed Apr. 15, 2005, which is a divisional of U.S.application Ser. No. 10/676,264, filed Oct. 2, 2003, now U.S. Pat. No.6,811,990, which claims priority of Japanese Patent Application No.2003-091972, filed Mar. 28, 2003, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor device including n-channel andp-channel MOS field effect transistors each having offset spacers orgate sidewall films on either side of a gate electrode and a method ofmanufacturing the same.

2. Description of the Related Art

In conventional MOS field effect transistors, an offset spacer or a gatesidewall film is formed on either side of a gate electrode. In order toconfigure such MOS field effect transistors, the same process is usedfor manufacturing both an n-channel MOS field effect transistor(hereinafter referred to as nMOSFET) and a p-channel MOS field effecttransistor (hereinafter referred to as pMOSFET) on the same substrate,as shown in FIGS. 1 to 5. This process will be described below.

Gate electrodes 101A and 101B are formed and then a film 102 isdeposited to serve as an offset spacer (see FIG. 1). Then, the film 102is processed to form offset spacers 102A and 102B on either side of thegate electrodes 101A and 101B, respectively (see FIGS. 1 and 2).Impurities are ion-implanted into the resultant structure to formextension regions 103A and 103B with each of transistor regions maskedby a resist film alternatively (see FIG. 3).

Then, a film 104 is deposited on the resultant structure to serve as agate sidewall film (see FIG. 4). Subsequently, the film 104 is processedto form a gate sidewall films 104A and 104B on the side of the offsetspacers 102A and 102B, respectively. Moreover, impurities areion-implanted to form source/drain regions 105A under protection of restof the transistor regions, then source/drain regions 105B are formedsimilarly (see FIG. 5).

Since the same process is used as described above, the offset spacers102A and 102B of the same thickness or the gate sidewall films 104A and104B of the same thickness are formed in both nMOSFETs and pMOSFETs. Itis however understood that the optimum thickness of the offset spacervaries between the nMOSFETs and pMOSFETs in these days of the progressof miniaturization of semiconductor devices. It is thus difficult tomake each of the nMOSFETs and pMOSFETs in predetermined characteristicswhen their offset spacers have the same thickness.

If a process from deposition to etching of a film serving as offsetspacers is performed only once, their thicknesses are the same. However,if the process is done two times, effective offset spacers of differentthicknesses can be formed. More specifically, first, a first offsetspacers are formed on either side of each of the gate electrodes of thenMOSFET and pMOSFET. Then, an extension region is formed in one of theMOSFETs. Next second offset spacers are formed on the first offsetspacers. After that, another extension region is formed in the otherMOSFET. Through the above process, the effective offset spacers can bevaried in thickness between the nMOSFET and pMOSFET (see, for example,K. Ohta and H. Nakaoka, “Double Offset Implantation Technique for HighPerformance 80 nm CMOSFET With Low Gate Leakage Current”, SEMI ForumJapan 2002, ULSI Technology Seminar, Section 4, pp. 42-47).

A process of forming offset spacers of effectively different thicknessesas described above will be described with reference to the drawings.

First offset spacers 102A and 102B are formed on the sides of gateelectrodes 101A and 101B, respectively. Then, impurities areion-implanted into the resultant structure with one of transistorregions to form an extension region 107 by protecting with a resist film106 on the other transistor region (see FIG. 6).

The resist film 106 is removed from the resultant structure and a film108, serving as a second offset spacer, is deposited on the structure(see FIG. 7). Then, the film 108 is processed and second offset spacers108A and 108B are formed on the sides of the first offset spacers 102Aand 102B, respectively. After that, an extension region 109 is formed inone transistor region by ion-implanting impurities into the resultantstructure while the other transistor region whose polarity is oppositeto that of the transistor region in the first ion implantation is beingprotected by the resist film (see FIG. 8).

In the foregoing process, however, the deposition of a film serving asoffset spacers has to be performed two times. Therefore, the variationsin the thickness of the offset spacers easily increase and those in thecharacteristics of the MOSFETs tend to increase. Since, moreover,etching for forming the offset spacers is performed two times, theamount of etching on the surface of the substrate increases at the timeof etching, and the MOS characteristics possibly deteriorate due to lossof implanted impurities. Furthermore, an undesirable excess offsetspacer is formed in the MOSFETs in which impurities are ion-implantedfirst; therefore, the above process is disadvantageous tominiaturization of semiconductor integrated circuits.

BRIEF SUMMARY OF THE INVENTION

A semiconductor device according to an aspect of the present inventioncomprises; a first impurity doped region of a second conductivity typeformed in a semiconductor substrate of a first conductivity type; asecond impurity doped region of the first conductivity type formed inthe semiconductor substrate of the first conductivity type; a first gateinsulation film formed on the first impurity doped region; a first gateelectrode formed on the first gate insulation film; a second gateinsulation film formed on the second impurity region; a second gateelectrode formed on the second gate insulation film; a first sidewallinsulation film formed on either side of the first gate electrode; asecond sidewall insulation film whose thickness differs from that of thefirst sidewall insulation film, the second sidewall insulation filmbeing formed on either side of the second gate electrode; a thirdsidewall insulation film formed on a side of the first sidewallinsulation film; and a fourth sidewall insulation film whose thicknessdiffers from that of the third sidewall insulation film, the fourthsidewall insulation film being formed on a side of the second sidewallinsulation film.

A method of manufacturing a semiconductor device according to anotheraspect of the present invention comprises: forming a first gateelectrode on a first impurity doped region of a second conductivity typein a semiconductor substrate a first conductivity type; forming a secondgate electrode on a second impurity doped region of the firstconductivity type in the semiconductor substrate; forming a firstinsulation film on the first and second gate electrodes and the firstand second impurity doped regions; introducing an element, which makes achange in the etching rate of the first insulation film, only into thefirst insulation film formed on the second impurity doped region and thesecond gate electrode; processing the first insulation film byanisotropic etching to form a first sidewall insulation film on eitherside of the first gate electrode and a second sidewall insulation filmon either side of the second gate electrode, the second sidewallinsulation film having a thickness different from that of the firstsidewall insulation film; forming a third impurity doped region of thefirst conductivity type in the first impurity doped region by ionimplantation using the first gate electrode and the first sidewallinsulation films as a mask; and forming a fourth impurity doped regionof the second conductivity type in the second impurity doped region byion implantation using the second gate electrode and the second sidewallinsulation films as a mask.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a cross-sectional view showing a first step of a conventionalmanufacturing process for a semiconductor device;

FIG. 2 is a cross-sectional view showing a second step of theconventional manufacturing process for a semiconductor device;

FIG. 3 is a cross-sectional view showing a third step of theconventional manufacturing process for a semiconductor device;

FIG. 4 is a cross-sectional view showing a fourth step of theconventional manufacturing process for a semiconductor device;

FIG. 5 is a cross-sectional view showing a fifth step of theconventional manufacturing process for a semiconductor device;

FIG. 6 is a cross-sectional view showing a first step of anotherconventional manufacturing process for a semiconductor device;

FIG. 7 is a cross-sectional view showing a second step of said anotherconventional manufacturing process for a semiconductor device;

FIG. 8 is a cross-sectional view showing a third step of said anotherconventional manufacturing process for a semiconductor device;

FIG. 9 is a cross-sectional view showing a structure of a semiconductordevice according to an embodiment of the present invention;

FIG. 10 is a cross-sectional view showing a first step of manufacturinga semiconductor device according to an embodiment of the presentinvention;

FIG. 11 is a cross-sectional view showing a second step of manufacturingthe semiconductor device according to the embodiment of the presentinvention;

FIG. 12 is a cross-sectional view showing a third step of manufacturingthe semiconductor device according to the embodiment of the presentinvention;

FIG. 13 is a cross-sectional view showing a fourth step of manufacturingthe semiconductor device according to the embodiment of the presentinvention;

FIG. 14 is a cross-sectional view showing a fifth step of manufacturingthe semiconductor device according to the embodiment of the presentinvention;

FIG. 15 is a cross-sectional view showing a sixth step of manufacturingthe semiconductor device according to the embodiment of the presentinvention;

FIG. 16 is a cross-sectional view showing a seventh step ofmanufacturing the semiconductor device according to the embodiment ofthe present invention; and

FIG. 17 is a cross-sectional view showing an eighth step ofmanufacturing the semiconductor device according to the embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described withreference to the accompanying drawings. The same components are denotedby the same reference numerals throughout the drawings.

First Embodiment

First, the structure of a semiconductor device according to a firstembodiment of the present invention will be described. FIG. 9 is across-sectional view of the structure of the semiconductor device inaccordance with the first embodiment.

As shown in FIG. 9, an n-type well region (n-type impurity semiconductorregion) 12 and a p-type well region (p-type impurity semiconductorregion) 13 are formed on a p-type semiconductor substrate 11. Anisolation insulating film 14 is formed between the n- and p-type wellregions 12 and 13.

Extension regions 15, each of which is a p-type impurity semiconductorregion, are formed separately from each other in an n-type well region12 serving as an element forming region between isolation insulatingfilms 14. Source/drain regions 16, which are a p-type impuritysemiconductor region, are formed outer side of each of the extensionregions 15. Further, extension regions 17, each of which is an n-typeimpurity semiconductor region, are formed separately from each other ina p-type well region 13 serving as another element forming regionbetween isolation insulating films 14. Source/drain regions 18, whichare an n-type impurity semiconductor region, are formed outer side ofeach of the extension regions 17.

A gate insulation film 19A is formed on the n-type well region 12between the source/drain regions 16, and a gate electrode 20A is formedon the gate insulation film 19A. Offset spacers 21A are formed on eitherside of the gate electrode 20A. Gate sidewall films 22A are formed onthe side of the offset spacers 21A.

A gate insulation film 19B is formed on the p-type well region 13between the source/drain regions 18, and a gate electrode 20B is formedon the gate insulation film 19B. Offset spacers 21B whose thicknessdiffers from that of the offset spacer 21A are formed on either side ofthe gate electrode 20B. Gate sidewall films 22B whose thickness differsfrom that of the gate sidewall films 22A are formed on the side of theoffset spacer 21B.

The offset spacer 21B is thinner than the offset spacer 21A. Forexample, the bottom portion of the offset spacer 21B, which contacts thesemiconductor substrate 11, is about 6 nm to 10 nm in thickness and thebottom portion of the offset spacer 21A, which contacts thesemiconductor substrate 11, is about 12 nm in thickness. The gatesidewall film 22B is thinner than the gate sidewall film 22A. Forexample, the bottom portion of the gate sidewall film 22A, whichcontacts the semiconductor substrate 11, is about 70 nm in thickness andthicker than the bottom portion of the gate sidewall film 22B whichcontacts the semiconductor substrate 11.

The offset spacers 21A and 21B are each made of an insulation film suchas a TEOS (tetraethylorthosilicate) film and a silicon nitride film. Theoffset spacer 21B includes an element that is not contained in theoffset spacer 21A and more specifically an element that enhances theetching rate. The element that enhances the etching rate is, forexample, arsenic (As), phosphorus (P), boron (B), indium (In), carbon(C) and germanium (Ge). The offset spacer 21B includes at least one ofthese elements.

The gate sidewall films 22A and 22B are each made up of an insulationfilm such as a multilayer film including a TEOS film, a silicon nitridefilm and a BSG (borosilicate glass) film. The gate sidewall film 22Bincludes an element that is not contained in the gate sidewall film 22Aand more specifically an element that enhances the etching rate. Theelement that enhances the etching rate is, for example, arsenic (As),phosphorus (P), boron (B), indium (In), carbon (C) and germanium (Ge).The gate sidewall film 22B includes at least one of these elements.

The gate electrode 20B includes an element that is not contained in thegate electrode 20A, for example, at least one of arsenic (As),phosphorus (P), boron (B), indium (In), carbon (C) and germanium (Ge).

A pMOSFET includes a n-type well region 12, extension regions 15,source/drain regions 16, a gate insulation film 19A, a gate electrode20A, offset spacers 21A and gate sidewall films 22A. An nMOSFET includesa p-type well region 13, extension regions 17, source/drain regions 18,a gate insulation film 19B, a gate electrode 20B, offset spacers 21B andgate sidewall films 22B.

In the semiconductor device described above, the offset spacers and/orthe gate sidewall films can be varied in thickness between the nMOSFETand pMOSFET. Thus each of the offset spacers and the gate sidewall filmsmay be optimized in thickness without deteriorating from predeterminedcharacteristics of nMOSFETs and pMOSFETs. In particular, the offsetspacers can be adjusted in thickness between the nMOSFET and pMOSFET andthus the location of the extension regions, which is formed on theunderside of the gate sidewall films formed outside of the offsetspacers, can be controlled. Accordingly, the characteristics of thenMOSFET and pMOSFET can be optimized.

Moreover, the offset spacer and the gate sidewall film, which wereundesirably thick, can be thinned. Further miniaturization of asemiconductor integrated circuit including the nMOSFETs and the pMOSFETscan be achieved.

Second Embodiment

A method of manufacturing the foregoing semiconductor device will now bedescribed as a second embodiment. FIGS. 10 to 17 are cross-sectionalviews each showing a step of manufacturing the semiconductor device.

Referring to FIG. 10, an isolation insulating film 14 is formed in ap-type semiconductor substrate 11 by such process as trench isolationand LOCOS isolation to define an element forming region. Impurities areion-implanted into the element forming region to form an n-type wellregion 12 and a p-type well region 13, respectively. As shown in FIG.11, a gate insulation film is formed on the element forming regions andthen a conductive film serving as a gate electrode, e.g., a polysiliconfilm, is deposited by CVD or the like. Furthermore, the polysilicon filmis processed by RIE to form gate structure including gate electrodes 20Aand 20B and gate insulation films 19A and 19B.

Referring to FIG. 12, an insulation film 21 serving as an offset spacer,e.g., a TEOS film or a silicon nitride film having a thickness of about9.5 nm, is formed on the structure shown in FIG. 11 by LPCVD or thelike.

Subsequently, a resistant film, which serves as a mask for an impurityintroduction, is formed on one of an nMOSFET region and a pMOSFETregion, and the other is opened. Then, at least one of impurity elementssuch as arsenic (As), phosphorus (P), boron (B), indium (In), carbon (C)and germanium (Ge) is introduced into the insulation film 21 in theopened region.

In the second embodiment, as shown in FIG. 13, an impurity element 24,e.g., at least one of arsenic (As), phosphorus (P), boron (B), indium(In), carbon (C) and germanium (Ge) is introduced into the insulationfilm 21 in the nMOSFET region by an ion implantation, while the pMOSFETregion is masked with a resist film 23. The conditions for the ionimplantation are as follows. When boron is ion-implanted, theacceleration voltage is 5 keV and the dose is 1.0×10¹⁵ cm⁻². Whenarsenic is ion-implanted, the acceleration voltage is 50 keV and thedose is 1.0×10¹⁵ cm⁻². When phosphorus is ion-implanted, theacceleration voltage is 15 keV and the dose is 1.0×10¹⁵ cm⁻². Theetching rate of the insulation film 21 on the element forming region ofthe nMOSFET into which the impurity 24 is introduced by the ionimplantation is enhanced.

After that, the resist film 23 is removed and the insulation film 21 isprocessed by an anisotropic etching such as RIE. Thus, as shown in FIG.14, offset spacers 21A are formed on either side of the gate electrode20A of the pMOSFET and offset spacers 21B, which are thinner than theoffset spacers 21A, are formed on either side of the gate electrode 20Bof the nMOSFET. Since the etching rate of the insulation film 21 on thenMOSFET region is higher than that of the insulation film 21 on thepMOSFET region, the offset spacers 21B become thinner than the offsetspacers 21A. As described above, for example, the thickness of thebottom portion of the offset spacer 21B, which contacts thesemiconductor substrate 11, is designed to be about 6 nm to 10 nm andthe thickness of the bottom portion of the offset spacer 21A, whichcontacts the semiconductor substrate 11, is designed to be about 12 nm.

If an impurity element that makes a change in the etching rate isintroduced only in the insulation film serving as an offset spacer onone of transistor regions as described above, offset spacers withdifferent thicknesses can be formed on both sides of each of the nMOSFETand pMOSFET in one deposition step of an insulation film and one etchingstep of the insulation film to form offset spacers.

Then, as shown in FIG. 15, after the nMOSFET region is masked with aresist film, impurities are ion-implanted into the surface of the n-typewell region 12 by using the gate electrode 20A and the offset spacer 21Aas a mask to form extension regions (p-type impurity semiconductorregions) 15 between which a channel region formed beneath the gateinsulation film 19A of the pMOSFET. Similarly, impurities areion-implanted into the surface of the p-type well region 13 by using thegate electrode 20A and the offset spacer 21B as a mask to form extensionregions (n-type impurity semiconductor regions) 17 between which achannel region formed beneath the gate insulation film 19B of thenMOSFET after the pMOSFET region is masked with a resist film.

Subsequently, as illustrated in FIG. 16, an insulation film 22 servingas a gate sidewall film, e.g., a multilayer film including a TEOS film,a silicon nitride film and a BSG film, is formed to the thickness ofabout 64 nm on the structure shown in FIG. 15 by LPCVD or the like.

Furthermore, at least one of impurity elements such as arsenic (As),phosphorus (P), boron (B), indium (In), carbon (C) and germanium (Ge) isintroduced into the insulation film 22 where one of an nMOSFET regionand a pMOSFET region is masked with a resistant film and the other isopened.

In the second embodiment, as shown in FIG. 17, an impurity element 26,e.g., at least one of arsenic (As), phosphorus (P), boron (B), indium(In), carbon (C) and germanium (Ge) is introduced into the insulationfilm 22 by the ion implantation where the pMOSFET region is masked witha resist film 25 and the nMOSFET region is opened. The etching rate ofthe insulation film 22 on the nMOSFET region into which the impurityelement 26 is introduced is enhanced.

After that, the resist film 25 is removed and the insulation film 22 isprocessed by an anisotropic etching such as RIE. Thus, as shown in FIG.9, a gate sidewall films 22A are formed on the offset spacers 21A oneither side of the gate electrode 20A in the pMOSFET and a gate sidewallfilms 22B are formed on the offset spacers 21B on either side of thegate electrode 20B in the nMOSFET. Since the etching rate of theinsulation film 22 on the nMOSFET region is higher than that of theinsulation film 22 on the pMOSFET region, the gate sidewall films 22Bbecome thinner than the gate sidewall films 22A. As described above, forexample, the thickness of the bottom portion of the gate sidewall film22A, which contacts the semiconductor substrate 11, is about 70 nm, andthe bottom portion of the gate sidewall film 22B, which contacts thesemiconductor substrate 11, is thinner than that of the gate sidewallfilm 22A.

If an impurity element that makes a change in the etching rate isintroduced in the insulation film serving as a gate sidewall film ononly one of transistor regions as described above, gate sidewall filmswith different thicknesses can be formed on both sides of each of thenMOSFET and pMOSFET in one deposition step of a gate sidewall insulationfilm and one etching step of the insulation film.

Then after the nMOSFET region is masked with a resist film, impuritiesare ion-implanted into the surface of the n-type well region 12 by usingthe gate electrode 20A, offset spacers 21A and gate sidewall films 22Aas a mask to form source/drain regions (p-type impurity semiconductorregion) 16 outer side of each extension regions 15 between which achannel region formed beneath the gate insulation film 19A of thepMOSFET. Similarly, impurities are ion-implanted into the surface areaof the p-type well region 13 by using the gate electrode 20B, offsetspacers 21B and gate sidewall films 22B as a mask to form source/drainregions (n-type impurity semiconductor region) 18 outer side of eachextension regions 17 between which a channel region formed beneath thegate insulation film 19B of the nMOSFET after the pMOSFET region ismasked with a resist film.

The semiconductor device shown in FIG. 9 is manufactured through thesteps described above.

In the manufacturing steps describe above, the deposition of theinsulation film 21 serving as an offset spacer is performed once and sois the etching of the insulation film 21 to form an offset spacer. Thevariation in the thickness of the offset spacer can thus be reducedagainst that in the case where the deposition and etching are eachperformed two times and more. Consequently, the variation in thelocation of the extension region formed using an offset spacer as amask, which is due to the variation in the thickness of the offsetspacer, can be decreased. As a result the variations in thecharacteristics of the MOSFET transistors can be reduced. Since,moreover, the offset spacers can be adjusted in different thicknessbetween the nMOSFET and pMOSFET, the extension regions can be formed inthe optimum position, outside of the offset spacers. Hence, thecharacteristics of the nMOSFET and pMOSFET can be optimized inpredetermined values.

Another advantage of the present invention is to reduce deteriorationsof MOSFETs due to a dose loss of doped impurities in a surface of theelement forming region. The does loss is caused by an undesired excessetching of the surface of the element forming region during theinsulation film etching to form offset spacers. An nMOSFET and a pMOSFETwith less variations in characteristics can be achieved by a processwith only one step of deposition and etching of insulation film to formoffset spacers against an nMOSFET and a pMOSFET produced by a processwith two and more steps of deposition and etching of insulation film toform offset spacers.

According to the method of manufacturing the semiconductor devicedescribed above, the offset spacers or the gate sidewall films can beadjusted in different thickness between the nMOSFET and pMOSFET withoutcausing the problem that the number of steps greatly increases, thevariations in the characteristics of MOSFETs increase due to theincrease in variations in the thickness of the offset spacers, or thecharacteristics of MOSFETs deteriorate due to the increase in the amountof etching for the substrate when the deposited film is etched to forman offset spacer. Accordingly, the characteristics of the MOSFETs caneasily be optimized. Furthermore, the offset spacers and the gatesidewall films, which were undesirably thick, can be thinned and thusthe semiconductor integrated circuit can be miniaturized further.

According to the first and second embodiments described above, there canbe provided a semiconductor device and a method of manufacturing thesemiconductor device in which the offset spacers or the gate sidewallfilms can be adjusted in different thickness between an nMOSFET and apMOSFET without causing the problem of a great increase in the number ofsteps, an increase in the variations of characteristics of MOSFETs orthe deterioration of characteristics.

The above-described embodiments can be executed alone or in combination.Each of the embodiments includes inventions in various stages and theseinventions can be extracted from appropriate combinations of a pluralityof components disclosed in the embodiments.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A method of manufacturing a semiconductor device, comprising: forminga first gate electrode on a first impurity doped region of a secondconductivity type in a semiconductor substrate of a first conductivitytype; forming a second gate electrode on a second impurity doped regionof the first conductivity type in the semiconductor substrate; forming afirst insulation film on the first and second gate electrodes and thefirst and second impurity doped regions; introducing an element, whichvaries an etching rate of the first insulation film, only into the firstinsulation film formed on the second impurity doped region and thesecond gate electrode; processing the first insulation film byanisotropic etching to form a first sidewall insulation film on eitherside of the first gate electrode and a second sidewall insulation filmon either side of the second gate electrode, the second sidewallinsulation film having a thickness different from that of the firstsidewall insulation film; forming a third impurity doped region of thefirst conductivity type in the first impurity doped region by ionimplantation using the first gate electrode and the first sidewallinsulation films as a mask; and forming a fourth impurity doped regionof the second conductivity type in the second impurity doped region byion implantation using the second gate electrode and the second sidewallinsulation films as a mask.
 2. The method according to claim 1, furthercomprising: forming a second insulation film on the semiconductorsubstrate after the third and fourth impurity doped regions are formed;introducing an element, which varies an etching rate of the secondinsulation film, only into the second insulation film formed on thesecond and fourth impurity doped regions and the second gate electrode;processing the second insulation film by anisotropic etching to form athird sidewall insulation film on the first sidewall insulation film onthe side of the first gate electrode and a fourth sidewall insulationfilm on the second sidewall insulation film on the side of the secondgate electrode, the fourth sidewall insulation film having a thicknessdifferent from that of the third sidewall insulation film; forming afifth impurity doped region of the first conductivity type in the firstimpurity doped region by ion implantation using the first gateelectrode, the first sidewall insulation film and the third sidewallinsulation film as a mask; and forming a sixth impurity doped region ofthe second conductivity type in the second impurity doped region by ionimplantation using the second gate electrode, the second sidewallinsulation film and the fourth sidewall insulation film as a mask. 3.The method according to claim 1, wherein the second sidewall insulationfilm is thinner than the first sidewall insulation film.
 4. The methodaccording to claim 2, wherein the fourth sidewall insulation film isthinner than the third sidewall insulation film.
 5. The method accordingto claim 1, wherein the element which varies the etching rate is anelement which enhances the etching rate.
 6. The method according toclaim 5, wherein the element which enhances the etching rate is at leastone of arsenic, phosphorus, boron, indium, carbon and germanium.
 7. Amethod of manufacturing a semiconductor device, comprising: formingfirst and second element forming regions in a semiconductor substrate ofa first conductivity type, the first and second element forming regionsbeing isolated from each other by an isolation region; forming a firstimpurity doped region of a second conductivity type in the first elementforming region; forming a second impurity doped region of the firstconductivity type in the second element forming region; forming firstand second gate insulation films on the first and second impurity dopedregions, respectively; forming first and second gate electrodes on thefirst and second gate insulation films, respectively; forming a firstinsulation film on the first and second gate electrodes and the firstand second impurity doped regions; introducing an element, which variesan etching rate of the first insulation film, only into the firstinsulation film formed on the second impurity doped region; and thesecond gate electrode; processing the first insulation film byanisotropic etching to form a first offset spacer on either side of thefirst gate electrode and a second offset spacer on either side of thesecond gate electrode, the second offset spacer having a thicknessdifferent from that of the first offset spacer; forming a firstextension region of the first conductivity type in the first impuritydoped region by ion implantation using the first gate electrode and thefirst offset spacer as a mask; and forming a second extension region ofthe second conductivity type in the second impurity doped region by ionimplantation using the second gate electrode and the second offsetspacer as a mask.
 8. The method according to claim 7, furthercomprising: forming a second insulation film on the first and secondimpurity doped regions and the first and second gate electrodes afterthe first extension region and the second extension region are formed;introducing an element, which varies an etching rate of the secondinsulation film, only into the second insulation film formed on thesecond impurity doped region and the second gate electrode; processingthe second insulation film by anisotropic etching to form a first gatesidewall film on the first offset spacer on the side of the first gateelectrode and a second gate sidewall film on the second offset spacer onthe side of the second gate electrode, the second gate sidewall filmhaving a thickness different from that of the first gate sidewall film;forming a first source/drain region of the first conductivity type inthe first impurity doped region by ion implantation using the first gateelectrode, the first offset spacer, and the first gate sidewall film asa mask; and forming a second source/drain region of the secondconductivity type in the second impurity doped region by ionimplantation using the second gate electrode, the second offset spacer,and the second gate sidewall film as a mask.